1. Field of the Invention
The invention relates to a method and means for filtering and intensifying electrical signals and more particularly to a method and means for filtering and intensifying weak signal components of predetermined desired period of repetition.
2. Description of the Prior Art
The method and means of the present invention have substantially unlimited application. For example, the present invention may be used to filter and amplify weak signals in association with radar, sonar, satellite tracking and the like.
The present invention is also well adapted to electrophysiologic research. In such an application the superimposing of effects of repetitive signals at fixed, relatively long periods of repetition, with concomitant relative cancellation of other periods of repetition, serves to record the responses at the desired period of repetition in magnified form with continuous response to changes in effect from cycle to cycle.
The method and means of the present invention may, for example, be used in brain studies to pick up and amplify signals from the brain normally masked by the total electric activity of the brain. Signals from the depth of the brain may be intensified and recorded from the surface of the head.
The present invention is also useful in chemical diagnosis and the like, wherein desired electrical signals generated by repetitive chemical actions in the body can be amplified and recorded.
Prior art workers have used a number of methods and a variety of apparatus to filter and amplify weak signals. For example, use has been made of computers such as a computer of average transients. A single recording head and a tape loop have been used to make multiple recordings of a signal initiated by a synchronizing signal. This is exemplified by U.S. Pat. No. 3,378,825. However, both of these methods and means are non-continuous, and neither is capable of continuously reproducing a weak signal in amplified form, showing changes in the signal from cycle-to-cycle.
U.S. Pat. No. 3,480,932 teaches an apparatus for increasing the signal-to-noise ratio of a recurring signal. The patent contemplates the use of a dual track closed loop magnetic tape or the like, an adder, a single recording head, a pickup head and an erasing head together with an auxiliary recording head, an auxiliary pickup head and an auxiliary erasing head. These auxiliary heads enable a synchronizing signal to be temporarily stored on the second track of the tape. This structure, however, does not make multiple recordings of a given signal which is intensified by summation as the signal is repeated and cannot continuously reproduce a weak signal in amplified form showing changes in the signal from cycle-to-cycle.
The present invention is directed to a method and means whereby the desired weak signal is simultaneously fed to a plurality of recording heads in such a way that the signals are superposed on a magnetic tape to continuously produce a recording of the desired signal with increased amplitude. Means may also be provided to reproduce the desired signal of increased amplitude through the use of a playback head and appropriate readout means.